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Old Dec 28, 2012, 12:25 PM
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United States, MI, Big Rapids
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Speed control as voltage regulator

Has anyone have any input on using a speed control to power an RX in a Gas powered Plane. So far I notice using a 25amp brushless speed control and a 3c 1000mah lipo to power the cdi on a 26cc it has way stronger and solid spark. My servos also seem to have a definate power increase as they respond quicker. I'm just curious of using this instead of a normal voltage regulator.
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Old Dec 28, 2012, 12:30 PM
I don't want to "Switch Now"
pmackenzie's Avatar
Toronto (Don Mills), Canada
Joined Dec 2002
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Unless you add an L-C filter to the output you are feeding the receiver short pulses of full battery voltage, not a continuous feed of lower voltage.

Do yourself and your equipment a favour and buy a BEC that lets you set the voltage you want.

Pat MacKenzie
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Old Dec 28, 2012, 12:30 PM
I think I'm inverted. Maybe.
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United States, CA, Pacifica
Joined Apr 2012
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Wait - are you saying using a built-in BEC on an ESC over a external voltage regulator or are you actually plugging in the Rx to the motor leads of the ESC?

If you're using the ESC's BEC:

Your servos might be snappier with a ESC BEC because the ESC BEC might be simply higher rated than your external BEC. The ESC BEC might be outputting a higher voltage or more current than the external BEC is.

There is hardly any difference between an external BEC and an ESC BEC. One is just on the same circuit board as an ESC, while the other isn't. The specs of both can be quite different.


If you're using the ESC's motor leads:

Don't.

Bascially, A brushless ESC controls power of a motor by outputting it's full voltage straight from the battery but pulsing it. Longer pulses of on and less off mean that the motor gets more power.

Your stuff is working faster because the ESC is basically a big complicated switch. Many times per second the voltage is turning on and off, and so while the stuff might work, the voltage fluctuation will probably kill your capacitors over time. The servos are working faster because they are getting unregulated voltage straight from the battery, but on and off many times per second.

Do yourself a favor and get yourself a external BEC. You can get BECs that run up to 6 volts, which will give you that snappier speed.
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Old Dec 28, 2012, 12:37 PM
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United States, MI, Big Rapids
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I have the speed control set up like you would on a ep plane. I don't have any of the acuall motor leads hooked to anything. I have a stead 6v going to my rx. I only have the speed control to knock down the power from the lipo to power my system. The motor leads are covered up not hooked to anything.
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Old Dec 28, 2012, 12:44 PM
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Joensuu, Finland
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That will work. Although most of the hardware of the esc are just sitting there doing nothing, but it will work and is not harmful in any way as long as you stay within bec current limit.
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Old Dec 28, 2012, 12:50 PM
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United States, MI, Big Rapids
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Thanks. I just figure it would be a good way to use my old speed controls I'm not using to convert my gas planes to be powered by lipo systems. They should be able to run my planes servos longer and not have a need to recharge so often.

I used my volt meter to test the voltage comming from the sc and it went straight to 6v and did'nt fluxuate at all no mater what I told the servos to do.

I though it would be ok as they run ep planes systems without any issues.
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Old Dec 28, 2012, 02:59 PM
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Rich in ILM's Avatar
USA, NC, Wilmington
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Quote:
Originally Posted by mrwrenchus View Post
Thanks. I just figure it would be a good way to use my old speed controls I'm not using to convert my gas planes to be powered by lipo systems. They should be able to run my planes servos longer and not have a need to recharge so often.

I used my volt meter to test the voltage comming from the sc and it went straight to 6v and did'nt fluxuate at all no mater what I told the servos to do.

I though it would be ok as they run ep planes systems without any issues.
It will work but most 25a esc's are only rated at 2 amps output and 3 to 4s battery max as they are, mostly linear supplies. That is not a lot of servo power if you are flying anyhting but small servos. It's an assured crash if the linear bec gives up.
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